I don't have enough knowledge to answer your first two questions, but as for the last two - lots of people are making new tribes and it's very welcome. Please check to make sure there isn't already an existing tribe for the exact interest - you can do this by searching various related terms with the search tool at the top of the page. Just make sure to click "tribes" after you've put in your search terms so that you'll see potentially relevant tribes and not just the relevant snaps.

As for promotion, /t/newtribes is all about promoting your new endeavour!